Girders In Everyday Life: They Aren’t Just Wood Trusses!
A “girder” truss is a truss consisting of 2 or more members coupled together and intended to handle exceptional loads; for instance those imposed by other trusses attached to it. Usually, these members have lumber of a larger dimension in the bottom chord to accommodate the connection of other trusses thru the use of “hangers”. These “girders” can be connected together with nails, specially designed screws, or bolts. The lumber used will be of a higher “grade” than standard trusses. The nail plates will be larger and sometimes made of a higher grade of steel.
The above is a representation and an explanation of what a wooden truss girder is. However, we see girders every day, in various forms that contradict the norm. Ever drive towards a small town on a riverbank and have to cross a bridge? A steel “A” shaped structure on both sides supports the roadbed. Those structures are also “girders”, albeit a different type. We see commercial buildings being erected with steel I-beams as supporting members spaced many feet apart. Each of those I-beams are technically girders because they support more than their own weight.
You may not realize that a rope bridge over a mountain gorge, has a form of a girder as well. Think about it. The supporting ropes are of a larger diameter than the ropes hanging down to support the planks you walk on. That’s the description of a girder.
Girders are everywhere. The roadways of the super highways we travel on pass over many other roadways before they reach their end. Many of these “bridges” are composed of “Box Girders” (hollow shapes of concrete and steel) which support the roadbed. Think of the entrances and exits of large cities, with their many over-lapping roadways, one above the other, which change traffic flow. Box girders in action.
In the component industry, girders are there in many forms. Common girders, #1 hip trusses, corner hip jacks, transitional trusses for L-shaped or T-shaped buildings. In some areas of the country, California for example, trusses labeled “Drag Struts” are used throughout a building to support the walls in the event of an earthquake. We use trusses, loaded with drywall material, as fire stops in multi-family dwellings. Above every door or window opening in a building, there is a type of girder called a “header” which spans the opening. Church steeples, roof dormers, chimney stacks, the list goes on, are all supported by girders.
We take them for granted, but girders are an important and necessary item in our everyday life. I could go on and on about the different types of girders I have seen in my 40 year career. But I need to keep this article under 500 words! So I will leave that up to you! How many other types of girders can you name?
Richard Gould – Design Administration
Gould Design, Inc.